This invention relates to dispenser pumps of the kind in which a pump chamber is defined between a piston and a cylinder, and in which in use liquid product enters the pump chamber through a valved inlet and leaves it through an outlet, optionally valved, leading to a discharge opening.
Pumps of the kind described are well known for use in small hand-operated dispensers where the pump is mounted on a container of a liquid product to be dispensed. Usually a pump body comprising the cylinder is a fixed component, which may be mounted in a neck of the container by means of a closure or securing cap. The piston is on the inner end of a plunger whose outer manually-engageable end projects from an opening in the body, and which is reciprocable in a pumping stroke to alter the volume of the pump chamber. The usual disposition, whether at rest or in operation, has the plunger projecting upwardly from the top of the pump body and the pump chamber inlet at the bottom of the pump body, drawing product by suction from the supply container interior beneath. So, for convenience of description herein, the expressions “top”, “upper” etc. are used to refer to positions and directions towards the direction of projection or extension of the plunger, although this particular orientation is not essential in practice, and the expressions “bottom”, “downwards” etc. are used analogously.
Usually the pump body comprises a generally cylindrical portion constituting the cylinder in which the piston moves. The pump components are typically of molded plastics materials. A pump spring is usually provided to urge the plunger towards its extended position, thereby automatically re-filling (priming) the pump chamber with product to be dispensed after each dispensing stroke. Most hand-operated dispensers are of the “moveable nozzle” type in which the outlet, outlet channel and discharge opening are in the plunger component. However some are of the “fixed nozzle” type in which the outlet from the pump chamber, like the inlet, is part of the pump body so that the discharge channel and discharge opening need not move when the plunger is operated. The present proposals are generally applicable to pump dispensers of the kinds described above.
In pump dispensers of the kinds described it is necessary to vent exterior air into the container to compensate for the volume of product dispensed, unless a collapsible container is used. Usually this venting is provided in the structure of the pump, so that the simplest possible standard containers can be used. One type of vent path admits air at an exterior vent opening of the pump body, typically at or adjacent to the point of emergence of the stem from the pump body, into a clearance between the stem and pump body/cylinder wall which is above the piston, i.e. outside the pump chamber, and then to one or more restricted vent openings out through (or around a top edge of) the cylinder wall to the container interior.
Typically the vent opening is provided by one or more small holes or slots through an upper region of the cylinder wall. A narrow and tortuous vent path is usually desirable because the compensation air need not enter quickly nor in large volume, whereas conversely it is important to avoid liquid product from escaping through the vent path if the dispenser is shaken or temporarily inverted.
It is also well known for dispensers of the kind described to have means for locking the plunger in its depressed/retracted position relative to the body (against the urging of the pump spring, where present) to make it compact for storage, shipping and display. Such dispensers are usually called “down-shippers”. Respective lock-down formations are provided on the plunger and pump body whereby when depressed the plunger can be turned to bring the formations into engagement and lock it down. Suitable lock-down formations include circumferentially-localized slots on one component through which a lug on the other component can pass and then be turned out of register with the slot, or cam formations such as partial or complete screw threads. Where the vent path passes between a plunger stem and a collar of the pump body, it can be arranged that part of the plunger blocks or plugs the corresponding clearance between stem and collar in the locked-down position, to prevent escape of liquid via the vent path e.g. during shipping.
One aspect of the present invention relates to sealing of the vent path in the extended position of the plunger. The vent path extends through a vent gap defined between the plunger stem and a collar portion of the pump body. Each of the plunger stem and the collar has a respective seal portion. They can be complementarily shaped. In the extended position of the plunger, the stem seal portion and the collar seal portion meet and seal against one another to block the vent path. Usually, this engagement also acts as a stop engagement which limits the movement of the plunger, i.e. defines the extended position.
Preferably at least one of the stem seal portion and the collar seal portion has a tapered shape whereby the portions are guided into a closely-fitting engagement. Preferably an edge of one seal portion meets a taper surface on the other. However, it is also possible to have taper surfaces on both, e.g. complementary tapers.
Additionally or alternatively one of the stem seal portion and the collar seal portion may comprise a flexible lip portion, or even a discrete resilient seal element, e.g. of elastomer. Or, the two seal portions may make a sliding plug fit, optionally with a guide taper to lead them together.
Most dispensers have a generally cylindrical symmetry with an axis of symmetry, and in this context the above-mentioned formations may all be annular around the axis, e.g. with substantially conically-tapering downward divergence of the stem and/or collar.
The piston is usually provided as a radial enlargement at the lower end of the plunger stem. The position of the stem seal relative to the plunger is selected in dependence on the position of the corresponding body collar through which the stem operates. It may be at a position spaced above the top surface of the piston. Or, it may be at a transition from the stem to the piston.
While it is preferred that the seal be provided on the stem, an alternative possibility is to provide a seal, to block the vent path in the manner described, on top of or at the top periphery of the piston part of the plunger, and engaging upwardly or inwardly against a correspondingly downwardly- or outwardly-directed pump body component, where the sealing between these components will block the vent path. Thus, the present proposals encompass a “plunger seal” in addition to the specific “stem seal” first described above. As mentioned, the position of transition between the stem and piston is a good location for the seal.
The up-position seal described above provides the following potential benefits, taking into account that once the dispenser starts to be used, it is conventionally left standing with its plunger spring-urged to the extended position rather than being locked down again. Should the dispenser (container and pump) be knocked over or dropped in this position, conventional dispensers are liable to leakage of product through the vent channels. This is particularly relevant when the liquid product contains volatile components, such as alcohol-based liquids for infection control. With their low surface tension and high vapor pressure, these liquids leak easily. They also tend to evaporate at room temperature, and sealing of the vent in the manner described can help to prevent loss of the volatile component and thereby maintain the intended product composition and flow properties.
Known dispensers often rely on the abutment of an upward shoulder on the plunger stem or piston against a downward formation of the pump body or collar as a stop for limiting the plunger extension stroke, but these have not constituted vent seals. Firstly, not all of these pumps have the vent path running through the corresponding clearance. Secondly, a stop engagement is conventionally provided by the meeting of generally axially-directed flat annular surfaces which, because of manufacturing tolerances, cannot provide a seal. However by adapting the respective engaging portions, e.g. as described above, a good sealing effect can be achieved without having to improve the manufacturing tolerances.
Another route for unintended escape of material is through the outlet passage from the pump chamber, which is re-filled with product after each dispensing stroke. We therefore prefer to use an outlet valve in which the valve member is resiliently urged against its seat by a valve spring. For example, a ball valve and a helical spring may be used. The combination of anti-leakage measures provides a valuable improvement.
While sealing of the vent path provides valuable inhibition of product leakage and evaporative loss, there are situations in which a full or absolute seal may be problematic. For example, if the product has a volatile component e.g. an alcohol, and is subjected to a rapid temperature increase, there could be a dangerous build-up of pressure even in the plunger-up condition. It would be desirable to relieve this via the vent path rather than via the outlet valve, since the latter route would cause some ejection of liquid product. The sealing surface adaptations mentioned above enable a close fit to be obtained. It therefore becomes practical, in a variant or refinement structure, to provide for a controlled degree of limited venting by means of one or more local slots or grooves in the surfaces of one or both of the stem seal portion and the collar seal portion mentioned above. A taper feature enables the components to be guided into close surface-to-surface engagement, so that the predetermined cross-section of the slot or groove is reliably defined as the available vent area. Being narrow and small, this provides for gradual release of gas pressure in high pressure situations, while still inhibiting evaporative loss under normal conditions, but resisting the passage of liquid product because of the high energy needed to overcome the viscous resistance and surface wetting which would be entailed in a liquid leakage flow.
The number and dimensions of such gas escape vents (slots or grooves) will be determined primarily with reference to the properties of the liquid product involved and the conditions in which the container is to be used.
The above features relate to the plunger-up condition. For a down-shipper pump, it is also desirable to provide a vent path seal for the locked-down (shipping) position of the plunger. It may be provided by a downwardly-directed shoulder or divergence or other sealing element on the plunger stem or at the plunger head, which seals against a corresponding upwardly-directed sealing feature of the pump body, perhaps, the same collar as used to make the up-position seal, when the plunger is locked down. It may use any of a tapered fit, plug fit or flexible lip (on either component), e.g. as described for the up-position seal.
In all aspects herein, the preferred pump is of the moveable-nozzle type, in which the plunger contains the discharge channel. Typically the plunger has a head with a laterally-projecting spout. As is known, the outlet valve can be positioned anywhere along the discharge channel from the opening at the piston to the discharge opening of the spout. When an outlet valve spring is used, as preferred, a convenient position for the outlet valve is in the head of the plunger adjacent an angled join between stem and spout portions thereof.
A pump spring, such as a conventional metal helical spring, is desirably provided to urge the plunger towards the extended (up) position. The spring may be in the pump chamber as is conventional, bearing down against the pump chamber floor and up against the piston end of the plunger stem. Or, if it is desired to avoid contact of a metal spring component with the product to be dispensed, the spring may instead be positioned outside (above) the pump chamber, acting between a lower abutment provided in the pump body at an intermediate height, and an upper abutment close beneath the plunger head.
A second aspect of the present invention, preferably combined with the other proposals but also of independent value, relates to dispenser pumps of the kind described in which the plunger can be locked down. Conventionally, the pump body lock-down formations are at or adjacent the point of emergence of the plunger stem, the plunger lock-down formations being on the immediate underside of the plunger head. What we propose here instead is to recess the lock-down engagement into the interior of the pump body. The lock-down formation of the stem is spaced below the head thereof, and at the extended position of the plunger does not emerge beyond the plunger body. A corresponding lock-down formation(s) of the body is provided at a position recessed down inside the body, to be engaged by the stem lock-down formation in the plunger-down position.
Thus, all the portion of stem that passes through the top body opening may be of generally uniform external cross-section. A seal or wiper member may thus be provided at the top of the body around this opening to act against the outer surface of the plunger stem. This top outer seal helps to keep the interior of the pump clean and free of grit entering from outside, while also helping to prevent product or vapor leakage from the interior. If, as is preferred, this top outer seal is used in combination with other features proposed herein, it acts in combination with them.
When such a top outer seal is present, the point of emergence of the stem from the body may be unsuitable as an entrance to the vent path. If so, one or more separate vent entrances may be formed through the top of the pump body, e.g. between the top outer seal element and the top of the pump body, and through into the vent path below the engagement of the top outer seal against the plunger stem.
The pump body lock-down formation(s) may be provided integrally on the interior of a cylinder body member which also provides the pump chamber-defining cylinder, or on a discrete component such as an insert housing such as described below. Preferred lock-down formations comprise cam formations, e.g. screw thread-type formations, because they can be progressively tightened to assure a locked-down seal.
A further independent aspect of the present invention, which again is advantageously combined with one or more or all of the other proposals herein, is a discrete insert housing which is part of the pump body. The pump body comprises a cylinder body member defining the pump cylinder at a lower portion thereof, i.e. the cylinder swept by the piston. The insert housing occupies an upper portion of the cylinder body member, and is a generally tubular component projecting down inside the body member. It has a generally cylindrical side wall and a floor with a central opening through which the plunger stem passes. Preferably it plugs or fits into the top of the cylinder body member from above, being secured usually by a snap or threaded union to the latter. At its lower end it may provide any one or more of                a support for the lower end of the pump spring,        a pump body lock-down formation,        a collar having a seal portion engageable with a corresponding stem seal portion to effect an up-position vent seal in accordance with the first proposal above,        a collar seal portion for engagement with a corresponding stem seal portion for a down-position vent seal as discussed above.        
For the function of vent definition and vent sealing, the insert housing wall should be a fully closed structure. Usually the vent opening through the cylinder body member wall is adjacent to the top thereof, and the insert housing extends down below it, so vent clearance or a vent path is defined between the outside of the insert housing and the inside of the body member wall. This clearance may be by means of a localised notch or groove in one or both components, but more preferably is a full annular clearance resulting from a difference in circular diameters.
A floor of the insert housing can provide a said collar for sealing or seal support at its inner periphery surrounding the stem. It may also provide a seat for the bottom end of the pump spring. A lock-down formation, such as one or more screw thread portions or one or more other cam or lug elements, may be provided as a radially inward projection(s) on the side wall of the insert housing.
In a preferred embodiment the plunger stem comprises a central stem tube inside a helical plunger spring, passing through the collar opening in the insert housing floor, and an outer skirt having the plunger lock-down formations at its lower extremity, with the spring extending in a radial clearance between the stem tube and the outer skirt.
Other features of the dispenser and pump may be conventional. For example, feed to the pump chamber may be through a conventional dip tube or other inlet, via a ball valve or other conventional inlet valve. The front of the piston may be designed to plug or block the pump chamber inlet opening in the lock-down position. The pump components may be held on the container by a retaining cap, e.g. a snap or threaded cap, having a central opening surrounded by an inward retaining flange. An outward flange around the top of the pump cylinder body member can be trapped down onto the top edge of the container neck by the retaining cap.
The pump and container may be made from conventional materials, or from special materials selected in accordance with the skilled person's knowledge when special technical needs arise.